The present disclosure relates generally to compounds for the treatment of angiogenesis-mediated diseases. More particularly, the present disclosure relates to cremastranone analogs and methods for synthesizing cremastranone analogs.
Angiogenesis does not occur in the body, except during development and wound repair processes. However, during numerous pathological conditions, angiogenesis occurs, notably in ocular diseases such as retinopathy of prematurity (ROP), diabetic retinopathy (DR), and “wet” age-related macular degeneration (AMD). After pathological angiogenesis occurs, newly formed blood vessels are fragile, porous and not fully differentiated. The formation of such new blood vessels in the eye may lead to hemorrhage, rapid photoreceptor degeneration, and eventual fibrotic scarring, with rapid, permanent vision loss.
Clinical symptoms of DR are seen in 75% of diabetic patients, with 10% of them eventually developing visual impairment. DR is currently the leading cause of blindness among working age adults and accounts for 8% of the legal blindness in the United States. Additionally, almost 2 million Americans are affected by AMD. AMD has an estimated loss of productivity burden of $5.4 billion annually in the United States. Severely affected patients have a very poor quality of life, comparable to that of catastrophic stroke victims or advanced cancer patients in constant pain.
Established treatment modalities for AMD include thermal laser photocoagulation or photodynamic therapy in conjunction with verteporfin. More recently, anti-vascular endothelial growth factor therapies such as pegaptanib, ranibizumab, aflibercept, and bevacizumab have shown success in slowing and even reversing vision loss in some age-related macular degeneration patients. But the significant acute, systemic side effects (non-ocular hemorrhage, myocardial infarction, and stroke) indicate that these therapies can act outside the eye even when delivered intravitreally. Blinding intraocular side effects are also possible and the long-term risks of these drugs are still unclear. Moreover, because they are biologics, the cost-benefit ratios of these drugs are unfavorable. For instance, ranibizumab costs approximately $2,000 per monthly dose, rendering these treatments unaffordable for many patients. Since recurrence after treatment cessation can also occur, treatment with drug combinations targeting different pathways that truly eradicate the disease has been touted as the future of therapy for this disease.
A similar situation exists for retinopathy of prematurity (ROP). Retinopathy of prematurity (ROP) is characterized by abnormal blood vessel growth in the neonatal retina. The disease develops in two stages. In the first, hyperoxic stage, from 22 to 30 weeks' gestational age, high oxygen levels (as experienced in the ventilated, extrauterine environment compared to in utero) lead to decreased VEGF production and subsequent cessation of vascularization. In the second phase, photoreceptors mature and the avascular retina grows and becomes hypoxic, prompting production of VEGF. VEGF is essential for signaling normal vessel growth during development, but when aberrantly expressed at high levels, causes improper neovessel growth. Neovessels, extending into the vitreous, do not oxygenate the retina well and easily rupture, leading to retinal ganglion cell and photoreceptor loss, retinal detachment, and blindness.
In 2010, 12% of children in the United States were born prematurely, and 1.5% were very low birth weight (VLBW; ≤1500 g). Almost 70% of these VLBW infants were likely to develop ROP, which is caused by aberrant angiogenesis after exposure to postnatal hyperoxia. The disease is estimated to cause visual loss in 1300 children per year in the United States, and severe visual impairment in a further 500 children per year. Overall, between 6% and 18% of childhood blindness is attributable to ROP. Moreover, as more and more children survive premature birth in middle income countries due to improvements in neonatal intensive care, ROP is becoming more prevalent worldwide. Aside from the acute risk of blindness, in childhood and even as adults, ROP survivors are more likely than the general population to develop posterior segment pathology, retinal detachment, myopia, amblyopia, strabismus, early cataract, and glaucoma.
Although biologic treatments are effective for retinopathy of prematurity and show fewer side effects than surgical treatments, there remain significant concerns about lasting toxic or developmental effects in neonates, especially since these drugs can have systemic actions even when delivered locally. Accordingly, there is a critical unmet need for novel small molecules to treat ocular neovascularization disorders as well as other angiogenesis-mediated diseases, to complement the existing approaches and allow lower-dose, combination therapies.
The bulb of the Orchidaceae family member Cremastra appendiculata (D. Don) is a traditional medicine in East Asia, used internally to treat several cancers, and externally for skin lesions. Several natural products have been extracted from this plant, but perhaps most intriguing of these is a compound known as cremastranone, previously known by the generic name “homoisoflavanone” (FIG. 1). Cremastranone 1,5,7-dihydroxy-3-(3-hydroxy-4-methoxybenzyl)-6-methoxychroman-4-one, is a member of a small group of known homoisoflavanones and has also been isolated from members of the Hyacinthaceae.
Cremastranone has been identified as the component of C. appendiculata bulbs responsible for a blockade of the proliferation of human umbilical vein endothelial cells (HUVECs) mediated via G2/M phase cell cycle arrest. Clues to cremastranone's anti-proliferative mechanism come from the discovery that the natural source compound induces expression of p21WAF1 (CDKN1A), an inhibitor of the cyclin-dependent kinase Cdc2 (CDK1), which in turn is down-regulated by cremastranone. Cremastranone also blocked prostaglandin synthesis from arachidonic acid in a microsome assay, without marked effects on function of cyclooxygenases 1 and 2 as purified enzymes. Inhibition of cyclooxygenase 2 expression may explain this finding, at least in keratinocytes exposed to UV radiation, a system in which cremastranone shows anti-inflammatory effects. In this context, cremastranone also decreased phosphorylation of the mitogen activated protein kinases (MAPKs), Jun N-terminal kinase (JNK), p38MAFK, and extracellular signal regulated kinase (ERK). It also blocked nuclear translocation of NF-κB, and production of cytokines TNF-α, IL-6 and IL-8, as well as of reactive oxygen species (ROS).
The natural cremastranone also inhibited angiogenesis in vivo. In the chick chorioallantoic membrane model, cremastranone was as effective as retinoic acid in blocking new vessel growth induced by bFGF. Cremastranone also showed efficacy in blocking pathogenic neovascularization in an oxygen-induced retinopathy model of retinopathy of prematurity and in the laser photocoagulation murine model of choroidal neovascularization. These models are widely used for treatment evaluations in these ocular neovascular disorders. Additionally, injection of 10 μM cremastranone into the vitreous of normal adult mice showed no cytotoxic or inflammatory effects on the retina, nor did it induce apoptosis of retinal cells.
Based on the foregoing, it would be highly advantageous to produce synthetic cremastranone and develop additional small molecule anti-angiogenic therapies to complement existing approaches for treatment of ocular and other neovascular disorders. It would be additionally beneficial, if these molecules performed as well, or better, than the natural cremastranone.